The present invention relates to a cabin pressure control system, especially for use in an aircraft, comprising at least one pressure sensor for measuring actual pressure inside a cabin, at least one outflow valve for controlling a pressure differential between said actual pressure and the pressure of an atmosphere surrounding said cabin, at least one controller for calculating a drive signal to be communicated to said at least one outflow valve based on the actual pressure and the atmosphere pressure or the pressure differential.
Additionally, the present invention relates to a method of controlling the actual pressure inside a cabin, especially in an aircraft cabin, comprising the steps of measuring the actual pressure inside said cabin, measuring the pressure in a surrounding atmosphere, calculating a pressure differential between said actual pressure and said atmosphere pressure, or, as alternative, measuring a pressure differential between said actual pressure and an atmosphere pressure, and communicating an actual pressure signal and an atmosphere pressure signal and/or a pressure differential signal to at least one controller for calculating a drive signal for at least one outflow valve for controlling the pressure differential between said actual pressure and said atmosphere pressure.
In yet another aspect, the present invention is directed to an outflow valve for controlling a pressure differential between actual pressure in a cabin and a surrounding atmosphere being provided with an input for receiving a drive signal from a controller and at least one drive, said outflow valve being suitable for use in a cabin pressure control system or a method as set forth above.
The pressure differential between the actual cabin pressure and atmosphere pressure may be calculated by measuring both pressures and subtracting them from each other. Alternatively, said pressure differential may be measured directly by a suitable sensor. It is of course possible to use information from other aircraft systems, too. The pressure differential is referred to as positive if cabin pressure is higher than atmosphere pressure and as negative if otherwise.
A controller, a cabin pressure control system and a method of controlling the actual pressure inside a cabin are known from EP 0 625 463 B1, issued to the applicant of the present application. Said prior art document discloses a cabin pressure control system comprising a controller, one outflow valve and two safety valves. The controller calculates an output signal based on the pressure differential between the cabin and the atmosphere and additional critical parameters like final cruise flight level. The outflow valve is actuated in order to keep the actual cabin pressure near a predetermined control cabin pressure. The known system provides a closed loop control.
The system must fulfill two requirements. First, the pressure differential must not exceed a certain threshold because otherwise the aircraft fuselage may be damaged or destroyed. Second, the operator usually sets a certain pressure rate of change which must be maintained. Huge change rates in cabin pressure are harmful for the crew and the passengers and therefore not acceptable.
In case of malfunction of the outflow valve or the controller, the pressure differential between the cabin pressure and the atmosphere pressure may exceed a predetermined threshold. In case of a positive pressure differential the safety valves open mechanically based on said pressure differential. Said opening prevents damage or destruction of the cabin due to the pressure differential. In order to compensate a negative pressure differential, the known system additionally provides a negative relief valve allowing entry of air in the cabin.
The known cabin pressure control system is reliable. However, it requires the use of one outflow valve and two safety valves to prevent overpressure, leading to an increased weight which is most undesirable in aircrafts. In the prior art cabin pressure control system two independent overpressure relief valves are required by aviation regulations.
Usually, prior art pressure control systems operate two control channels with one additional manual lane. In case of failures the systems stepwise degrades to simplex and to the manual back-up. The required autonomous safety functions are implemented in the safety valves.
New requirements for enhanced safety of the unique systems, especially stipulated by FAR amendments will no longer accept this prior art cabin pressure control systems. The redundancy level must be increased. Moreover, the operators of aircrafts have demanded a higher dispatchability of control systems which has affected the system architecture in terms of the probability for the need to replacing defective components.
It is therefore an object of the present invention to provide a cabin pressure control system, a method of controlling cabin pressure and an outflow valve allowing effective pressure control and preventing undue high cabin pressure with reduced weight and increased redundancy. It is a further object of the present invention to maintain the highly sophisticated cabin pressure control even if one or several components of the cabin pressure control system fail.
To achieve said objects, the invention proposes in a first embodiment a cabin pressure control system of the above mentioned kind which is characterized in that said at least one outflow valve is connected to said at least one controller and said at least one pressure sensor in order to receive both the drive signal from said at least one controller and an actual pressure signal from said at least one pressure sensor. To advantage, said cabin pressure control system comprises several controllers, several sensors for cabin pressure and several outflow valves which are connected to each other. All controllers, sensors and outflow valves can then exchange signals by means of a common data exchange line.
In a second embodiment, the above mentioned objects are achieved by a cabin pressure control system as set forth above which is characterized in that said at least one pressure sensor, said at least one outflow valve and said at least one controller are connected to each other by a common data exchange line in order to exchange signals with each other.
In a preferred embodiment, the cabin pressure control system comprises at least one additional sensor for measuring atmosphere pressure. Said sensor may be configured as integral part of the cabin pressure control system and connected to the common data exchange line. As alternative, the sensor for measuring atmosphere pressure may be connected to the at least one controller. In that case, the sensor may be part of a different avionic system, e.g. a system for determining flight parameters.
The data exchange line may be configured as duplex bus system and preferably features a triple redundancy. It may be connected to a control board for information output and instruction input by an operator.
All major functions of the new cabin pressure control system are preferably triplex. They may be connected to each other with the triple redundant full duplex bus system. Said system is preferably time synchronized. Data synchronization and symmetrization is performed between each of the components connected to the bus.
Contrarily to the prior art systems there is no longer a channel in control directing the associated drives for said channel of all outflow valves. Contrarily, the invention provides pressure control which will be performed by those components which are selected from an arbitration logic. The components in charge may vary in each major time frame of the real time control function.
In case of failure in one function there is no system degradation like the loss of one channel in prior art systems. Only said function is faulty or suspected to be inaccurate. It may be replaced by another component effecting the same function. If the failure can be recovered, the defective component will come back to operation based on the results of a built-in test logic.
The invention still provides a manual mode of operation which will be implemented as a function running on the already existing control system resources. There is no need to allocate extra system resources for the manual mode function. The components and the bus need not to be modified.
Introduction of the bus allows for high flexibility of the cabin pressure control system. Defective components are disconnected from the bus and may be easily replaced. Additional components may be added without sophisticated changes in system architecture.
The method in accordance with the invention is characterized by the fact that said actual pressure signal additionally is communicated to said at least one outflow valve for controlling the pressure differential between said actual pressure and said atmosphere pressure in order to keep said pressure differential between a predetermined upper and a predetermined lower level. Additionally, the atmosphere pressure signal may be communicated to said at least one outflow valve. To advantage, there are again provided several controllers, pressure sensors and outflow valves which are exchanging information by means of a common data exchange line. Each controller may calculate his own drive signal. The drive signal of all controllers are then compared to each other in order to determine any inaccurate calculations. Additionally, the outflow valves receive pressure information and may check accuracy of the drive signals received by the controllers.
In a preferred embodiment the positions of drive units of each outflow valve are monitored and communicated to other outflow valves and/or the controllers. Malfunction of a drive unit may be determined on data exchange between the ourflow valves without involving the controllers. Any inaccurate positions can be readily determined. The power supply to an outflow valve with an inaccurate drive unit position may be switched off. Preferably, the outflow valves exchange information regarding the positions of their drive units by means of the common data exchange line. As alternative, there may be provided a separate data exchange channel.
The positions of the drive units of all outflow valves are controlled by the controller which is currently in charge. Said controller may communicate with the other controllers, the sensors and the outflow valves. The system may automatically change the controller which is in charge.
If the controller in charge issues an incorrect drive signal, said inaccuracy is recognized. Control and calculation of the drive signal is transferred to another controller. There will be no system degradation.
The outflow valve in accordance with the invention is characterized by the fact that it additionally comprises an input for receiving the actual pressure signal and at least one logic unit for actuating its drive unit. Contrarily to the prior art outflow valves, the invention provides an outflow valve with its own logic unit. Said logic unit is preferably less complex than the controller logic units. It provides a safety backup in case all controllers fail and constantly monitors the drive signals received from the controller in charge. To that end, the outflow valve is provided with an input for receiving the actual pressure signal.
To further enhance the redundancy the outflow valve preferably comprises a further input for an atmosphere pressure signal and/or a differential pressure signal. It may additionally or as alternative be provided with an input-output for connection to a common data exchange line. All relevant information may be communicated to each outflow valve. The logic units receive all required information for actuating their associated drive units. Said actuation signal and the drive unit position are constantly monitored and compared with drive signals of the controller.
The outflow valve may to advantage comprised two drive units. There may be provided a single logic unit for actuating all drive units. As alternative, each drive unit may be provided with its own logic unit. In the latter case, the logic units of each outflow valve communicate with each other. Communication may be effected by means of the common data exchange line or by a direct data exchange channel between the logic units inside the outflow valve.